Timing and amount of southern Cascadia earthquake subsidence over the past 1700 years at northern Humboldt Bay, California, USA

Stratigraphic, lithologic, foraminiferal, and radiocarbon analyses indicate that at least four abrupt mud-over-peat contacts are recorded across three sites (Jacoby Creek, McDaniel Creek, and Mad River Slough) in northern Humboldt Bay, California, USA (∼44.8°N, −124.2°W). The stratigraphy records subsidence during past megathrust earthquakes at the southern Cascadia subduction zone ∼40 km north of the Mendocino Triple Junction. Maximum and minimum radiocarbon ages on plant macrofossils from above and below laterally extensive (>6 km) contacts suggest regional synchroneity of subsidence. The shallowest contact has radiocarbon ages that are consistent with the most recent great earthquake at Cascadia, which occurred at 250 cal yr B.P. (1700 CE). Using Bchron and OxCal software, we model ages for the three older contacts of ca. 875 cal yr B.P., ca. 1120 cal yr B.P., and ca. 1620 cal yr B.P. For each of the four earthquakes, we analyze foraminifera across representative mud-over-peat contacts selected from McDaniel Creek. Changes in fossil foraminiferal assemblages across all four contacts reveal sudden relative sea-level (RSL) rise (land subsidence) with submergence lasting from decades to centuries. To estimate subsidence during each earthquake, we reconstructed RSL rise across the contacts using the fossil foraminiferal assemblages in a Bayesian transfer function. The coseismic subsidence estimates are 0.85 ± 0.46 m for the 1700 CE earthquake, 0.42 ± 0.37 m for the ca. 875 cal yr B.P. earthquake, 0.79 ± 0.47 m for the ca. 1120 cal yr B.P. earthquake, and ≥0.93 m for the ca. 1620 cal yr B.P. earthquake. The subsidence estimate for the ca. 1620 cal yr B.P. earthquake is a minimum because the pre-subsidence paleoenvironment likely was above the upper limit of foraminiferal habitation. The subsidence estimate for the ca. 875 cal yr B.P. earthquake is less than (<50%) the subsidence estimates for other contacts and suggests that subsidence magnitude varied over the past four earthquake cycles in southern Cascadia.

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Minimal stratigraphic evidence for coseismic coastal subsidence during 2000 yr of megathrust earthquakes at the central Cascadia subduction zone

Geosphere ◽

10.1130/ges02254.1 ◽

2020 ◽

Author(s):

Alan R. Nelson ◽

Andrea D. Hawkes ◽

Yuki Sawai ◽

Ben P. Horton ◽

Rob C. Witter ◽

...

Keyword(s):

Transfer Function ◽

Sea Level ◽

Function Analysis ◽

Detection Threshold ◽

Cascadia Subduction Zone ◽

Tsunami Deposit ◽

Diatom Assemblages ◽

14C Dating ◽

Megathrust Earthquakes ◽

Transfer Function Analysis

Lithology and microfossil biostratigraphy beneath the marshes of a central Oregon estuary limit geophysical models of Cascadia megathrust rupture during successive earthquakes by ruling out >0.5 m of coseismic coastal subsidence for the past 2000 yr. Although the stratigraphy in cores and outcrops includes as many as 12 peat-mud contacts, like those commonly inferred to record subsidence during megathrust earthquakes, mapping, qualitative diatom analysis, foraminiferal transfer function analysis, and 14C dating of the contacts failed to confirm that any contacts formed through subsidence during great earthquakes. Based on the youngest peat-mud contact’s distinctness, >400 m distribution, ∼0.6 m depth, and overlying probable tsunami deposit, we attribute it to the great 1700 CE Cascadia earthquake and(or) its accompanying tsunami. Minimal changes in diatom assemblages from below the contact to above its probable tsunami deposit suggest that the lower of several foraminiferal transfer function reconstructions of coseismic subsidence across the contact (0.1–0.5 m) is most accurate. The more limited stratigraphic extent and minimal changes in lithology, foraminifera, and(or) diatom assemblages across the other 11 peat-mud contacts are insufficient to distinguish them from contacts formed through small, gradual, or localized changes in tide levels during river floods, storm surges, and gradual sea-level rise. Although no data preclude any contacts from being synchronous with a megathrust earthquake, the evidence is equally consistent with all contacts recording relative sea-level changes below the ∼0.5 m detection threshold for distinguishing coseismic from nonseismic changes.

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ASSESSING TEMPORAL VARIABILITY OF COASTAL DEFORMATION DURING MEGATHRUST EARTHQUAKES AT THE CASCADIA SUBDUCTION ZONE USING A DIATOM BAYESIAN TRANSFER FUNCTION

10.1130/abs/2020am-353769 ◽

2020 ◽

Author(s):

Isabel Hong ◽

◽

Niamh Cahill ◽

Simon E. Engelhart ◽

...

Keyword(s):

Transfer Function ◽

Subduction Zone ◽

Temporal Variability ◽

Cascadia Subduction Zone ◽

Megathrust Earthquakes

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Supplemental Material: Minimal stratigraphic evidence for coseismic coastal subsidence during 2000 yr of megathrust earthquakes at the central Cascadia subduction zone

10.1130/geos.s.13157825.v1 ◽

2020 ◽

Author(s):

A.R. Nelson ◽

et al.

Keyword(s):

Transfer Function ◽

Subduction Zone ◽

Tidal Marsh ◽

Cascadia Subduction Zone ◽

Radiocarbon Age ◽

Megathrust Earthquakes ◽

Sampling Locations ◽

Data Summaries

Includes tables and imagery showing core and sampling locations; figures showing stratigraphy at additional sites and results of transfer function reconstructions of elevation using diatom floras from core S; tables of foraminiferal and diatom data; summaries of previous investigations; the tidal marsh setting of our study site; methods of measuring sampling elevations; explanation of variance added to radiocarbon age errors; and listing of code for OxCal radiocarbon age models.

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Supplemental Material: Minimal stratigraphic evidence for coseismic coastal subsidence during 2000 yr of megathrust earthquakes at the central Cascadia subduction zone

10.1130/geos.s.13157825 ◽

2020 ◽

Author(s):

A.R. Nelson ◽

et al.

Keyword(s):

Transfer Function ◽

Subduction Zone ◽

Tidal Marsh ◽

Cascadia Subduction Zone ◽

Radiocarbon Age ◽

Megathrust Earthquakes ◽

Sampling Locations ◽

Data Summaries

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The Upper Limit of Barnacles as an Index of Sea-Level Change on the New England Coast during the past 100 Years

The Journal of Geology ◽

10.1086/627015 ◽

1964 ◽

Vol 72 (5) ◽

pp. 580-600 ◽

Cited By ~ 6

Author(s):

Clifford A. Kaye

Keyword(s):

New England ◽

Sea Level ◽

Sea Level Change ◽

Level Change ◽

The Past ◽

Upper Limit

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FORAMINIFERAL TRANSFER FUNCTION FOR HIGH-RESOLUTION SEA-LEVEL RECONSTRUCTION DURING HOLOCENE IN SUNDA SHELF, OFF MALAYSIA WATERS

10.1130/abs/2020am-355942 ◽

2020 ◽

Author(s):

Fatin Izzati Minhat ◽

◽

Nazihah Azmi ◽

Nur Hidayah Roseli ◽

...

Keyword(s):

High Resolution ◽

Transfer Function ◽

Sea Level ◽

Sunda Shelf

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A maximum rupture model for the central and southern Cascadia subduction zone—reassessing ages for coastal evidence of megathrust earthquakes and tsunamis

Quaternary Science Reviews ◽

10.1016/j.quascirev.2021.106922 ◽

2021 ◽

Vol 261 ◽

pp. 106922

Author(s):

Alan R. Nelson ◽

Christopher B. DuRoss ◽

Robert C. Witter ◽

Harvey M. Kelsey ◽

Simon E. Engelhart ◽

...

Keyword(s):

Subduction Zone ◽

Cascadia Subduction Zone ◽

Megathrust Earthquakes ◽

Rupture Model

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Hydroclimate variability in the low-elevation Atacama Desert over the last 2500 yr

Climate of the Past ◽

10.5194/cp-8-287-2012 ◽

2012 ◽

Vol 8 (1) ◽

pp. 287-306 ◽

Cited By ~ 44

Author(s):

E. M. Gayo ◽

C. Latorre ◽

C. M. Santoro ◽

A. Maldonado ◽

R. De Pol-Holz

Keyword(s):

Hydrological Cycle ◽

Atacama Desert ◽

Plant Macrofossils ◽

Central Andes ◽

Tropical Pacific ◽

Riparian Ecosystems ◽

Independent Evidence ◽

Radiocarbon Dates ◽

Climate Fluctuations ◽

The Past

Abstract. Paleoclimate reconstructions reveal that Earth system has experienced sub-millennial scale climate changes over the past two millennia in response to internal/external forcing. Although sub-millennial hydroclimate fluctuations have been detected in the central Andes during this interval, the timing, magnitude, extent and direction of change of these events remain poorly defined. Here, we present a reconstruction of hydroclimate variations on the Pacific slope of the central Andes based on exceptionally well-preserved plant macrofossils and associated archaeological remains from a hyperarid drainage (Quebrada Maní, ∼21° S, 1000 m a.s.l.) in the Atacama Desert. During the late Holocene, riparian ecosystems and farming social groups flourished in the hyperarid Atacama core as surface water availability increased throughout this presently sterile landscape. Twenty-six radiocarbon dates indicate that these events occurred between 1050–680, 1615–1350 and 2500–2040 cal yr BP. Regional comparisons with rodent middens and other records suggest that these events were synchronous with pluvial stages detected at higher-elevations in the central Andes over the last 2500 yr. These hydroclimate changes also coincide with periods of pronounced SST gradients in the Tropical Pacific (La Niña-like mode), conditions that are conducive to significantly increased rainfall in the central Andean highlands and flood events in the low-elevation watersheds at inter-annual timescales. Our findings indicate that the positive anomalies in the hyperarid Atacama over the past 2500 yr represent a regional response of the central Andean climate system to changes in the global hydrological cycle at centennial timescales. Furthermore, our results provide support for the role of tropical Pacific sea surface temperature gradient changes as the primary mechanism responsible for climate fluctuations in the central Andes. Finally, our results constitute independent evidence for comprehending the major trends in cultural evolution of prehistoric peoples that inhabited the region.

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